This is in addition to this post: Can't compile rwd skin SCSS in Magento CE 1.9
Windows 8.1 / PowerShell Compass 1.0.1 (Polaris) Sass 3.4.6 (Selective St
This appears to be a known issue with Sass 3.4.6. You'll need to downgrade to 3.4.5 until this is fixed.